Results of segregation analyses support the possibility that risk of Early Onset Periodontitis (EOP) may be due to a single major gene. Alternatively, several genes of moderate effect may contribute significantly to increasing risk of the disease. We conducted linkage analyses spanning the entire human genome to evaluate these hypotheses. Families with two or more close relatives affected by EOP were ascertained in the state of Virginia, and the country of Chile. DNA was extracted from blood and highly polymorphic markers distributed throughout the human genome were typed using the polymerase chain reaction. Linkage analyses were performed using a dominant model of disease transmission which is most strongly supported by the segregation analysis studies, as well as additional analyses based on assumptions of alternative modes of disease gene transmission. We also applied nonparametric methods of inferring linkage and/or linkage disequilibrium which do not require assumptions about the disease's genetic architecture. We have nearly completed these statistical analyses and have found several chromosomal regions with statistically significant evidence of linkage or linkage disequilibrium. These include the interleukin-1 region, which was reported to be associated with levels of severity in adult onset periodontitis. Clinical subject recruitment will continue to be through long-standing collaborations with periodontists in Virginia and Chile. An additional collaborative study, relevant to periodontal diseases, is the study of smoking cessation carried out at the Jerry L. Pettis Memorial Veterans Administration (VA) Medical Center in Loma Linda, California. As a supplement to an ongoing VA protocol, ambulatory veterans from the VA Preventive Medicine Clinic and the VA Stop Smoking Classes are being recruited to participate in this two-pronged study to test whether immunoglobulin levels change after smoking cessation and to evaluate possible hereditary influences on smoking behaviors.